The present invention generally pertains to injection molding of cable ties, and is particularly directed to methods that facilitate removal of a cable tie from the mold parts.
A cable tie may be used for bundling together articles such as cables or the like by forming and locking a closed loop around the articles. Cable ties also have other uses. Cable ties are also known as cable straps, cable clamps, cable clips, bundling ties, bundling straps, bundling clips, bundle ties, bundling belts, wire ties, ring clamps, adjustable clamps, harnessing devices, strap seals, binding straps, and ties. A cable tie includes a locking head, a strap extending from the head and terminating in a tip for passing through an opening in the head, and ratchet teeth on at least one side of the strap, wherein the locking head includes a pawl having teeth with surfaces for engaging the ratchet teeth to lock the strap in the locking head after the tip end of the strap has been pulled through the opening in the head. A cable tie may or may not include additional components; and the strap may have two or more sides, one, some or all of which include ratchet teeth. Examples of cable ties are described in U.S. Pat. Nos. 3,739,429; 3,924,299; 3,965,538; 4,473,524; 4,573,242 and 5,372,773.
Cable ties are manufactured economically by a cyclic injection molding method, in which molten plastic material is injected into a mold cavity defining the cable tie and then allowed to solidify within the mold cavity. The mold parts defining the mold cavity are then separated and the cable tie is removed from the mold parts. A preferred plastic material for cable ties is nylon, although other plastic materials may be used.
One method of injection molding a typical cable tie, as described above, that facilitates removal of the cable tie from the mold parts is described in U.S. Pat. No. 5,372,773. Such method includes the steps of:
(a) forming the cable tie by injecting molten plastic material into a mold cavity defined by a first mold part combined with a second mold part, wherein the first mold part includes a head region defining a portion of the head of the cable tie and the second mold part includes a tip region defining a portion of the tip of the cable tie;
(b) separating the first mold part from the second mold part while retaining said portion of the head of the cable tie in the head region of the first mold part and said portion of the tip of the cable tie in the tip region of the second mold part, to separate the head from the second mold part, to separate the tip from the first mold part, and to separate a major portion of the strap of the cable tie from the first and second mold parts;
(c) further separating the first mold part from the second mold part while still retaining said portion of the head of the cable tie in the head region of the first mold part to thereby remove said portion of the tip of the cable tie from the tip region of the second mold part; and
(d) subsequent to step (c), removing the head of the cable tie from the head region of the first mold part.
The present invention provides a method of injection molding a cable tie having a locking head, a strap extending from the head and terminating in a tip for passing through an opening in the head, and ratchet teeth on at least one side of the strap, wherein the locking head includes a pawl having teeth with surfaces for engaging the ratchet teeth to lock the strap in the locking head after the tip end of the strap has been pulled through the opening in the head, the method comprising the steps of
(a) forming the cable tie by injecting molten plastic material into a mold cavity defined by a first mold part combined with a second mold part, wherein the first mold part includes a head region defining a portion of the head of the cable tie and the second mold part includes a tip region defining a portion of the tip of the cable tie;
(b) separating the first mold part from the second mold part while retaining said portion of the head of the cable tie in the head region of the first mold part and said portion of the tip of the cable tie in the tip region of the second mold part, to separate the head from the second mold part, to separate the tip from the first mold part, and to separate a major portion of the strap of the cable tie from the first and second mold parts;
(c) further separating the first mold part from the second mold part while still retaining said portion of the tip of the cable tie in the tip region of the second mold part;
(d) removing said portion of the head of the cable tie from the head region of the first mold part; and
(e) subsequent to steps (c) and (d), ejecting the tip of the cable tie from the tip region of the second mold part.
In another aspect of the present invention, subsequent to step (b), the previously retained portion of the head of the cable tie is ejected from the head region of the first mold part while still retaining a portion of the tip of the cable tie in the tip region of the second mold part.
In still another aspect of the present invention, subsequent to step (b), the first mold part is further separated from the second mold part while still retaining a portion of the tip of the cable tie in the tip region of the second mold part to thereby remove the previously retained portion of the head of the cable tie from the head region of the first mold part.
In yet another aspect of the present invention, in which the plastic material is injected through a gate located in either the first mold part or the second mold part, subsequent to separation of the first and second mold parts, the previously retained portion of the head or the previously retained portion of the tip is ejected by using at least one ejector pin located in the one of the first or second mold parts in which the gate is not located.
In still a further aspect of the present invention, in which the plastic material is injected through a gate located in the first mold part, an undercut located in the second mold part is used to retain a portion of the tip of the cable tie in the tip region of the second mold part as the first and second mold parts are separating from one another.
In yet still a further aspect of the present invention, in which the mold parts define a strap region for forming the portion of the strap that extends between the head and the tip of the cable tie; and in which the plastic material is injected through a gate located adjacent either the tip region or the head region, an undercut located in the strap region of the one of the first or second mold parts in which the tip region or the head region that is adjacent the gate is not located is used to pull at least a portion of the strap from the portion of the strap region defined by the one of the first or second mold parts in which the tip region or the head region that is adjacent the gate is located, as the first and second mold parts are separating from one another.
Additional features of the present invention are described with reference to the detailed description of the preferred embodiments.